A256823 - OEIS

A256823

Numbers n such that A257378(n)=A257379(n), so the prime numbers k*n*2^n-1 and k*n*2^n+1 are twin primes for the smallest k such that k*n*2^n-1 is a prime number.

%I #23 Sep 15 2019 04:06:43

%S 4,7,9,11,27,40,63,80,120,173,227,358,445,525,767,1164,2180,5368,7898

%N Numbers n such that A257378(n)=A257379(n), so the prime numbers k*n*2^n-1 and k*n*2^n+1 are twin primes for the smallest k such that k*n*2^n-1 is a prime number.

%C The k values are in A257378 and A257379.

%o (PARI) a8(n) = my(k=1); while(!isprime(k*n*2^n+1), k+=2); k;

%o a9(n) = my(k=1); while(!isprime(k*n*2^n-1), k+=2); k;

%o isok(n) = a8(n) == a9(n); \\ _Michel Marcus_, Sep 15 2019

%Y Cf. A257378, A257379.

%K nonn,more

%O 1,1

%A _Pierre CAMI_, Apr 24 2015